PrEP is being scaled up for adolescent girls and young women (AGYW) as a way to prevent the unacceptably high HIV incidence in this group in South and East Africa. While PrEP is a highly effective intervention, its efficacy is threatened by non-adherence ? it only works if AGYW take it. In order to use and adhere to PrEP, AGYW need to understand their potential risk for acquiring HIV, believe in the use of PrEP for prevention, and be able to navigate to get PrEP and continue PrEP. Unfortunately, these steps are not easy for AGYW, and particularly those at highest risk for HIV. Thus, it is critical to determine what levels of adherence will be in demonstration projects of PrEP in AGYW. In addition, it is important to understand whether user factors and health care worker counseling influences PrEP adherence. We are currently conducting projects that involve delivering PrEP in public sector maternal child health (MCH) and family planning (FP) clinics. These projects involve understanding programmatic systems to deliver PrEP to women, including AGYW. We propose to leverage these projects to understand adherence in AGYW. Using the Information-Motivation-Behavior Model, we propose in AIM 1: to conduct longitudinal analyses to discern patterns of adherence (both with self-reported data and drug level monitoring), and identify correlates of adherence (including knowledge about PrEP, HIV risk perception, depression, and self-efficacy). Qualitative evaluation of women with consistently high adherence, intermittent adherence or consistently low adherence will be undertaken to understand personal narratives underlying adherence patterns. In AIM 2, we propose to adapt our mHealth SMS platform (Mobile WACh-X) to understand issues facing AGYW on PrEP. In our previous studies, 2-way SMS result in active engagement of AGYW, with conversations that discuss social and health issues relevant to medications. We hypothesize that this 2-way interactive SMS approach provides a tool to amplify ascertainment of `real-time real-life' issues relevant to PrEP use beyond what can be ascertained at routine clinic visits. In AIM 3, we propose to use simulated patients (SPs) trained in scripted scenarios to pose as AGYW who will evaluate health care workers' (HCWs) approach to counseling AGYW ? specifically, HCW empathy, information, decision-advice, and advice regarding PrEP adherence. In addition, SPs will work with HCWs in training sessions to evaluate and refine HCW counseling and youth friendly skills. This study will provide a unique multi-dimensional evaluation of PrEP adherence in AGYW and provide insights and tools to improve PrEP adherence in this at-risk population.